Such horizontal bore holes can be created using powered boring rams (also known as moles). Generally, these comprise a tubular body including a reciprocal hammer enabling the ram to self-propel through the ground by compressing the soil surrounding the cavity or bore created. In preferred versions, the ram is capable of reversing its direction of operation, so that during use it can e.g. back away from an obstruction such as a tree root. Examples of such reversible rams are described in GB 2111565 and WO 89/06736.
The simpler boring rams can only move in a straight line direction (whether in forward or reverse mode), so that the only control an operative has over the flight or path taken, is its initial alignment into the ground. They are in this way limited in terms of maneuverability, as there is no or little scope for changing the flight of the ram where for example, the ram is diverted from its initial or intended path by the presence of an obstacle. This is a problem particularly in stony soil or where there is much buried debris, for which a common and very inefficient solution is to dig up the ram to re-align it.
One approach to this problem is described in EP 0301287 and GB 2386142 which describe rams capable of non-linear travel. These rams include an angled head (or tail) which allow the ram to be steered through an arc. In one version, the tubular body of the ram is rotated about its axis during use to achieve the turning effect in the desired direction. As may be expected, the radius of turn achieved is primarily dependent on the size of the body of the ram. Typically the radius of the arc is in the order of tens of meters. A significant distance may be unnecessarily traveled when this is not required, after alignment deflection. Also, such steerable arc rams produce considerable soil disturbance and displacement in use.
They are therefore not ideal for use where there is little room to manoeuvre. For example, shallow service ducts used for telecommunications optical fibre in the access network leading to customer premises are located a short distance below the surface of customers' front gardens or under residential street pavements. The creation of such shallow ducts requires care to ensure the ram stays underground and does not break through the ground surface. For example, the requirement of the National Joint Utilities Group of the UK is that telecommunications cables deployed within the footpath are placed with 250 to 350 mm ground coverage from the surface.
It would therefore be desirable to be able to alter the flight of a boring ram during use in a minimally-disruptive manner.